1. Field of the Invention
This invention relates generally to a method and apparatus that allows for stimulation of body tissue, particularly sacral nerves. More specifically, this invention relates to an implantable medical electrical lead having at least one stimulation electrode adapted to be implanted near the sacral nerves for stimulation of a bundle of sacral nerve fibers and a fixation mechanism for providing chronic stability of the stimulation electrode and lead. Moreover, this invention relates to the method of implantation and anchoring of the medical electrical lead electrodes in operative relation to a selected sacral nerve to allow for stimulation.
2. Description of Related Art
Pelvic floor disorders such as, urinary incontinence, urinary urge/frequency, urinary retention, pelvic pain, bowel dysfunction (constipation, diarrhea), erectile dysfunction, are bodily functions influenced by the sacral nerves. Specifically, urinary incontinence is the involuntary control over the bladder that is exhibited in various patients. Incontinence is primarily treated through pharmaceuticals and surgery. Many of the pharmaceuticals do not adequately resolve the issue and can cause unwanted side effects, and a number of the surgical procedures have a low success rate and are not reversible. Several other methods have been used to control bladder incontinence, for example, vesicostomy or an artificial sphincter implanted around the urethea. These solutions have drawbacks well known to those skilled in the art. In addition, some disease states do not have adequate medical treatments.
The organs involved in bladder, bowel, and sexual function receive much of their control via the second, third, and fourth sacral nerves, commonly referred to as S2, S3 and S4 respectively. Electrical stimulation of these various nerves has been found to offer some control over these functions. Several techniques of electrical stimulation may be used, including stimulation of nerve bundles within the sacrum. The sacrum, generally speaking, is a large, triangular bone situated at the lower part of the vertebral column, and at the upper and back part of the pelvic cavity. The spinal canal runs throughout the greater part of the sacrum. The sacrum is perforated by the anterior and posterior sacral foramina that the sacral nerves pass through.
Neurostimulation leads have been implanted on a temporary or permanent basis having at least one stimulation electrode positioned on and near the sacral nerves of the human body to provide partial control for bladder incontinence. Temporary sacral nerve stimulation is accomplished through implantation of a temporary neurostimulation lead extending through the skin and connected with a temporary external pulse generator as described for example in commonly assigned U.S. Pat. Nos. 5,957,965 ad 6,104,960. A permanent neurostimulator is implanted if stimulation is efficacious and it is possible to do so in the particular patient. Permanent implantation is accomplished by implanting a permanent neurostimulation lead, extending the proximal portion of the lead body subcutaneously, and connecting its proximal end with an implantable pulse generator (IPG) implanted subcutaneously.
For example, U.S. Pat. Nos. 4,771,779, 4,607,739 and 4,739,764 disclose implanting an electrode on at least one nerve controlling the bladder and applying nerve stimulation energy to the nerve through the electrode. Electrodes positioned within the sacrum to control bladder function are also disclosed in U.S. Pat. No. 4,569,351.
In one embodiment, a lead bearing a distal stimulation electrode is percutaneously implanted through the dorsum and the sacral foramen (a singular foramina) of the sacral segment S3 for purposes of selectively stimulating the S3 sacral nerve. The lead is advanced through the lumen of a hollow spinal needle extended through the foramen, the single distal tip electrode is positioned adjoining the selected sacral nerve. Stimulation energy is applied through the lead to the electrode to test the nerve response. The electrode is moved back and forth to locate the most efficacious location, and the lead is then secured by suturing the lead body to subcutaneous tissue posterior to the sacrum and attached to the output of a neurostimulator IPG. Despite the suture fixation, sacral nerve stimulation leads having a single discrete tip electrode can be dislodged from the most efficacious location due to stresses placed on the lead by the ambulatory patient. A surgical intervention is then necessary to reposition the electrode and affix the lead.
The current lead designs used for permanent implantation to provide sacral nerve stimulation through a foramen have a number, e.g., four, ring-shaped, stimulation electrodes spaced along a distal segment of the lead body adapted to be passed into or through the foramen along a selected sacral nerve. Each distal stimulation electrode is electrically coupled to the distal end of a lead conductor within the elongated lead body that extends proximally through the lead body. The proximal ends of the separately insulated lead conductors are each coupled to a ring-shaped connector element in a proximal connector element array along a proximal segment of the lead body that is adapted to be coupled with the implantable neurostimulation pulse generator or neurostimulator IPG.
Again, the electrode array is moved back and forth with respect to the sacral nerve while the response to stimulation pulses applied through one or more of the electrodes is determined. The IPG is programmed to deliver stimulation pulse energy to the electrode providing the optimal nerve response, and the selection of the electrodes can be changed if efficacy using a selected electrode fades over time due to dislodgement or other causes.
Electrical stimulation pulses generated by the neurostimulator IPG are applied to the sacral nerve through the selected one or more of the stimulation electrodes in either a unipolar or bipolar stimulation mode. In one unipolar stimulation mode, the stimulation pulses are delivered between a selected active one of the stimulation electrodes and the electrically conductive, exposed surface of the neurostimulator IPG housing or can providing a remote, indifferent or return electrode. In this case, efficacy of stimulation between each stimulation electrode and the neurostimulator IPG can electrode is tested, and the most efficacious combination is selected for use. In a further unipolar stimulation mode, two or more of the stimulation electrodes are electrically coupled together providing stimulation between the coupled together stimulation electrodes and the return electrode.
In a bipolar stimulation mode, one of the distal stimulation electrodes is selected as the indifferent or return electrode. Localized electrical stimulation of the sacral nerve is effected between the active stimulation electrode(s) and the indifferent stimulation electrode.
A problem associated with implantation of permanent and temporary neurostimulation leads involves maintaining the discrete ring-shaped electrode(s) in casual contact, that is in location where slight contact of the electrode with the sacral nerve may occur or in close proximity to the sacral nerve to provide adequate stimulation of the sacral nerve, while allowing for some axial movement of the lead body.
Typically, physicians spend a great deal of time with the patient under a general anesthetic placing the leads due to the necessity of making an incision exposing the foramen and due to the difficulty in optimally positioning the small size stimulation electrodes relative to the sacral nerve. The patient is thereby exposed to the additional dangers associated with extended periods of time under a general anesthetic. Movement of the lead, whether over time from suture release or during implantation during suture sleeve installation, is to be avoided. As can be appreciated, unintended movement of any object positioned proximate a nerve may cause unintended nerve damage. Moreover reliable stimulation of a nerve requires consistent nerve response to the electrical stimulation that, in turn, requires consistent presence of the stimulation electrode proximate the sacral nerve. But, too close or tight a contact of the electrode with the sacral nerve can also cause inflammation or injury to the nerve diminishing efficacy and possibly causing patient discomfort.
Once the optimal electrode position is attained, it is necessary to fix the lead body to retard lead migration and dislodgement of the electrodes from the optimal position employing sutures or a sacral lead fixation mechanism of the types described in the above-referenced '351 patent or an improved fixation mechanism of the type described in commonly assigned U.S. Pat. No. 5,484,445. However, it is desirable to avoid use of complex fixation mechanisms that require surgical exposure large enough to implant the fixation mechanism, in these cases requiring exposure and attachment to the sacrum.
Once fixation is completed, the proximal lead body is typically bent at about 90° and tunneled subcutaneously to a remote site where its proximal connector elements are coupled to the neurostimulator IPG which is then implanted at the remote site. In this process some axial and lateral dislodgement of the stimulation electrodes can also occur.
It is generally desirable to minimize surgical trauma to the patient through surgical exposure of the tissue and sacrum and use of sutures or fixation mechanisms to hold the electrodes in place. It is preferred to employ a minimally invasive, percutaneous approach in a path extending from the skin to the foramen that the neurostimulation lead is extended through.
The above-referenced '965 patent describes one such percutaneous approach for implantation of a temporary neurostimulation lead that extends through the patient's skin 10 and is attached to an external pulse generator. Typically, the external pulse generator and exposed portion of the lead body are taped to the skin to inhibit axial movement of the lead body. When a stimulation time period ends, the lead is removed through the skin by application of traction to the exposed lead body, and the incision is closed. The neurostimulation lead bodies of the '965 patents are formed with surface treatment or roughening in a portion proximal to the neurostimulation electrode expected to extend from the foramen to the patient's skin that is intended to increase the resistance to unintended axial dislodgement of the lead body to stabilize the electrode. A length of the lead body is formed with indentations or spiral ridges or treated to have a macroscopic roughening. These surface treatments or geometries provide some acute fixation against the subcutaneous tissues, but they are necessarily insufficient to resist intentional retraction of the lead to remove it upon cessation of temporary stimulation.
The prior art discloses a number of configurations of implantable medical electrical leads other than neurostimulation leads that employ fixation mechanisms to maintain a stimulation electrode in relation to a body organ or tissue. Cardiac pacing leads are commonly provided with passive fixation mechanisms that non-invasively engage heart tissue in a heart chamber or cardiac blood vessel or active fixation mechanisms that invasively extend into the myocardium from the endocardium or epicardium. Endocardial pacing leads having pliant tines that provide passive fixation within interstices of trabeculae in the right ventricle and atrial appendage are well known in the art as exemplified by U.S. Pat. Nos. 3,902,501, 3,939,843, 4,033,357, 4,236,529, 4,269,198, 4,301,815, 4,402,328, 4,409,994, and 4,883,070, for example. Such tined leads typically employ three or four tines that extend outwardly and proximally from a band proximal to a distal tip pace/sense electrode and that catch in natural trabecular interstices when the distal tip electrode is advanced into the atrial appendage or the ventricular apex. Certain spinal cord stimulation leads have been proposed employing tines and/or vanes as stand-offs to urge the stimulation electrode in the epidural space toward the spinal cord as disclosed in U.S. Pat. Nos. 4,590,949 and 4,658,535, for example, and to stabilize the stimulation electrode in the epidural space as disclosed in U.S. Pat. No. 4,414,986, for example,
In the case of the '843 patent that was directed to the first atrial tined leads, longitudinally extending rows of elongated tines were provided within a 270° arc extending away from a distal tip electrode canted in the remaining 90° section. The multiple rows of tines were intended to lodge in the trabecular interstices and force the canted tip against the atrial endocardial wall. However, it was found in practice that the canted tip is unnecessary and that only three, much shorter, tines in the 270° arc or four tines spaced apart by 90° in a common circumference like a ventricular tined lead, are sufficient. The rows of tines shown in the '843 patent are necessarily closely spaced because of the small area of trabeculae in the right atrium, and more proximal tines simply typically do not engage anything and make it difficult to lodge any of the tines in the interstitial spaces.
Such endocardial tined leads are typically introduced from a puncture site of the venous system to the cardiac site employing a stiffening stylet with a tip that can be formed with a curve extended down the lead lumen to advance it through the venous system and into the heart chamber. Percutaneous lead introducers are used to access the puncture site. The tines fold against the introducter lumen and the vein wall after the lead distal end exits the introducer lumen. However, the above-referenced '070 patent does describe thin, webbed, or scalloped tines adapted to be introduced through an introducer already advanced all the way into a heart chamber.
In certain cases, sensing leads that include electrogram (EGM) sense electrodes are implanted subcutaneously and coupled to implantable cardiac monitors. One such cardiac monitoring system as shown in U.S. Pat. No. 5,313,953, for example, employs elongated electrode supports at the distal ends of leads that are tunneled subcutaneously into a sense electrode array and affixed with sutures sewn through pre-formed suture holes to subcutaneous tissue. First and second rows of projections also extend outwardly and proximally from the opposed first and second side walls of the electrode supports whereby the projections are in a common plane with the sense electrode. It is expected that tissue growth will occur around the projections and stabilize the lead. However, it can also be seen that the leads are advanced subcutaneously between tissue layers expanded by tunneling. The projections would likely not engage tissue during the acute phase before they are encapsulated. For this reason, the elongated leads are sutured in place to maintain the electrode position until the projections are encapsulated by tissue ingrowth. Furthermore, it is less critical to maintaining exact positioning of the sense electrodes of such a subcutaneous cardiac monitor than maintaining stimulation electrodes in the implanted positions for cardiac or nerve or muscle stimulation because minute stimulation electrode movement can decrease efficacy and increase battery energy consumption or fail.
Accordingly, there remains a need in the art for a permanently implantable electrical sacral nerve stimulation lead that is capable of being passed percutaneously over a guide wire, and/or through the lumen of an introducer from the patient's skin to locate stimulation electrodes in casual contact with a sacral nerve, that provides acute fixation with muscle and tissue layers posterior to the sacrum, and that can be bent to extend subcutaneously to the neurostimulator IPG without disturbing the fixation so that the stimulation electrodes are less likely to be dislodged during the acute recovery phase and the chronic implantation period.